a) Field of the Invention
The present invention relates to a tone signal synthesizer employing a delayed feedback type tone signal synthesizing algorithm, in which a driving waveform signal is inputted into a closed loop containing a delay circuit and a filter and the driving waveform signal is circulated in the closed loop to synthesize a tone signal after waveform processing.
b) Description of the Prior Art
In a waveform read type tone signal synthesizer, tone signals different in pitch are synthesized by reading a fundamental waveform (for example, a sinusoidal waveform) at different reading velocity. Because the number of points sampled from the fundamental waveform decreases as the frequency increases, the characteristics of the synthesized tone signals deteriorate. Further, it is difficult to change the signal waveform with the passage of time.
Japanese Patent Publication (JP-B) No. Sho-58-58679 has proposed a technique in which a driving waveform signal is inputted into a closed loop formed by connecting a filter and a delay circuit and the driving waveform signal is repeatedly circulated in the closed loop so that a tone signal is synthesized. The total delay time of the closed loop determines the repetition frequency. The characteristic of the filter determines frequency distribution of the signal characterizing the musical tone. According to this technique, the amplitude, high-frequency content, high-frequency phase, etc. of the signal can be changed widely with the passage of time, so that musical tones more perfectly approaching the musical tones of natural musical instruments can be generated compared with the waveform read type tone signal synthesizer.
In the conventional tone signal synthesizing technique, however, the synthesized musical tone is still not very rich in variation compared with the musical tone of a natural musical instrument, failing to attain a desired effect.